Hi,
I think while refactoring the DFDL schemas a little more, I came up with an
idea on how we can support inheritance with DFDL:
* In all cases with inheritance, we have a “choice” element in the schema
* Some sort of “type” element is parsed before the choice element itself
Now the idea is that if a type contains a choice, that the name of the base
class of all sub-types is based on the name of the element that contains the
choice.
Example:
<xs:complexType name="S7RequestMessage">
<xs:sequence>
<!-- Reserved value always 0x0000 -->
<xs:element name="reserved" type="s7:short" fixed="0"/>
<xs:element name="tpduReference" type="s7:short"/>
<xs:element name="parametersLength" type="s7:short"/>
<xs:element name="payloadsLength" type="s7:short"/>
<xs:element name="parameters" minOccurs="0"
dfdl:lengthKind="explicit" dfdl:lengthUnits="bytes"
dfdl:length="{../parametersLength}"
dfdl:occursCountKind="expression"
dfdl:occursCount="{if(../parametersLength gt 0) then 1 else
0}">
<xs:complexType>
<xs:sequence>
<xs:element name="parameter" maxOccurs="unbounded">
<xs:complexType>
<xs:sequence>
<xs:element name="type" type="s7:byte"/>
<xs:choice
dfdl:choiceDispatchKey="{xs:string(type)}">
<xs:element dfdl:choiceBranchKey="240"
name="s7GeneralParameterSetupCommunication"
type="s7:S7GeneralParameterSetupCommunication"/>
<xs:element dfdl:choiceBranchKey="4"
name="s7RequestParameterReadVar"
type="s7:S7RequestParameterReadVar"/>
<xs:element dfdl:choiceBranchKey="5"
name="s7RequestParameterWriteVar"
type="s7:S7RequestParameterWriteVar"/>
</xs:choice>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
In this case we would have an S7RequestMessage type which contains a property
“parameters” of type “List<Parameter>”.
Parameter (containing a choice) would be an abstract class with an abstract
“getDenominator” method.
S7GeneralParameterSetupCommunication would extend Parameter.
You think that’s a path to go? … Had to add some artificial elements in order
to set the boundaries of the types.
Chris
